<p>A catalyst system capable of catalysing the carbonylation of an olefinally unsaturated compound is described. The 5 catalyst system is obtainable by combining: (a) a metal of Group VIB or Group VIII B or a compound thereof; and (b) a bidentate phosphine of general formula (I) Ad)<SUB>s</SUB>(CR<SUP>4</SUP>R<SUP>5</SUP>R<SUP>6</SUP>)<SUB>T</SUB>Q<SUP>2</SUP>-A-(K,D)Ar(E,Z)-B-Q<SUP>1</SUP>(Ad)<SUB>u</SUB>(CR<SUP>1</SUP>R<SUP>2</SUP>R<SUP>3</SUP>)<SUB>v</SUB>. Ad represents an optionally substituted adamantyl radical bonded to the phosphorous atom via any one of its tertiary carbon atoms. A method of production of the catalyst is also illustrated.</p>
